When a Back-UPS UPS flashes the On-Line and Overload LEDs alternately, it is signifying that the unit is in ""Sleep"" mode after the optional shutdown software has gracefully shutdown the operating system. In this state the unit
turns off its output power to conserve the battery as the unit waits for normal input power to return. When power returns and is deemed safe for your equipment the UPS will then ""wake-up"" and turn back on its output power.
Normally, it is the optional shutdown software (PowerChute Personal Edition, PowerChute Business Edition) that commands the UPS to go to sleep once it has gracefully shutdown the operating system.
It is possible and normal, however, for the UPS under certain circumstances to go to sleep even though no optional shutdown software is being used in conjunction with the UPS. There are two possible scenarios that can cause the UPS to spontaneously go into ""Sleep"" mode.

1. If the UPS's battery is disconnected and reconnected while the UPS is operating On-Battery (4 beeps every 30 seconds, yellow On-Battery LED is illuminated) this will occur.

2. If the battery is disconnected while the unit is On-Line and then the UPS goes to battery (either because of a power problem or because the UPS's input power cord is unplugged) this will also occur.

Turning the unit off and back on with the battery connected will clear this symptom.